Generally, the shape of stator made of laminated silicon steel and the ratio of slots (the ratio between the slots and poles) of a conventional motor are similar to each other. Now, a nine-slot stator made of laminated silicon steel in a motor is used as an example for technical description.
Referring to FIG. 1, which is a top view a stator made of laminated silicon steel in a conventional motor, in which both side ends 11 of the armature tooth 1 were not trimmed as shown in FIG. 1. In that case, a slot effect will take place among the teeth thereof when the rotor is turning. The slot effect will result in the taking place of a cogging torque, which can cause a cogging pause; i.e., an unsteady running phenomenon to cause the motor to vibrate during running. Furthermore, the aforesaid phenomenon will worsen when the motor is running under a high frequency condition, wherein the stability of the motor will be reduced considerably.
The aforesaid defects caused by the slot effect can usually be solved by a technical method of magnetization. However, such method of magnetization for improving the cogging torque and other defects is to have the magnetic flux changed to a sine wave form so as to obtain a round and smooth magnetic force for reducing the slot effect.
However, the direct magnetization method is difficult to reduce the slot effect to a minimum or cause it to cease to exist. Furthermore, the magnetizing process is not easy to control. In case even a minor mistake is made, a considerable cogging torque may be reduced, but then the slot effect might become worse. In other words, the method of magnetization for reducing the slot effect needs further improvement.